Ethnobotanical Survey of Plants Used for Treating Cough Associated with Respiratory Conditions in Ede South Local Government Area of Osun State, Nigeria

In many developing countries, community members depend on their local flora for treating diverse ailments including those affecting the respiratory system. This is often attributed to the high cost and limited access to health care facilities. This present study focused on the documentation of plant species used against cough associated with the respiratory diseases in Ede South Local Government Area of Osun State. The survey was conducted using semi-structured interviews among 100 participants. Information obtained was analyzed using different ethno-botanical indices including relative frequency of citation (RFC) and fidelity level (FL). A total of 87 plant species from 39 families, which was mostly represented by Fabaceae, were reported in the study area. Crinum jagus was the most popular plant used against cough and approximately 32% of the plants have been reported as cough remedies for the first time. However, some of the documented plants have been reported for the treatment of cough and related respiratory diseases in several countries. In terms of the life-form, trees constituted the highest proportion of the medicinal plants (37%), while leaves (36%) were the predominant plant part prescribed for cough. Decoction was the main method of preparing the plants, which were all administered orally. Approximately 63% of the plants were exclusively sourced from the wild. The current study revealed the richness and widespread use of plant species for managing cough associated with respiratory diseases in the study area. The generated inventory contributes to the expanding database of valuable plant resources with medicinal potential in Nigeria and Africa.


Introduction
Respiratory diseases entail conditions such as chronic obstructive pulmonary disease (COPD), asthma, occupational lung diseases, and pulmonary hypertension [1]. Globally, these diseases affect millions of people across diverse ages and account for significant levels of disability and mortality especially in children less than 5 years [2][3][4][5]. The occurrence and severity of respiratory diseases remain high in both developed and developing countries. For instance, it remain one of the four major contributors to mortality and morbidity, resulting in high health cost and loss in productivity in developed countries [4]. Likewise, the disease burden associated with respiratory infections continues to increase in developing countries. Respiratory diseases often arise as a result of air

Field Interview Methods
Semi-structured questionnaires were used to obtain the ethnobotanical information from the participants from April to August, 2017. The questionnaire was designed to capture the following information of plants used for the treatment of cough associated with respiratory diseases; local name, used plant part(s) and preparation method. Bio-data of the participants including their age, gender, residence, occupation, and educational background were also recorded. The participants were purposively selected comprising herb-sellers, traditional medical practitioners (herbalist), farmers, and hunters in the area. They were informed of the concept of the study in order to seek their consent and willingness to participate in the survey. The participants were individually questioned on their knowledge of using plant species to treat cough associated with respiratory diseases. Ten native field assistants were engaged to administer and interpret the questions to the participants in their local language (Yoruba) in order to facilitate efficient communication.
Sixty-five men and 35 women (to make-up the 100 participants) were interviewed on their knowledge about cough and its management in the study area. The majority of the participants were males (65%) and mostly herbalists (35%) in terms of their occupation (Table 1). The population of the study area is estimated at 76,035 comprising of 39,385 males and 36,654 females [39]. The area is predominantly occupied by the Yoruba-speaking ethnic group. The study area as part of Ede region has drainage systems that ranged from open water bodies (dams, reservoirs and lakes) to rivers, streams, springs, wells, run-off waters and swamp/wetlands [40]. This inevitably influences the micro-climate and vegetation in the study area, which is considered as rain forest [41]. The people in the study area are mostly farmers owing to the availability of green vegetation [42]. Although 70% of the population are living in the villages, the remaining 30% reside in town, engaging in commercial services.

Field Interview Methods
Semi-structured questionnaires were used to obtain the ethnobotanical information from the participants from April to August, 2017. The questionnaire was designed to capture the following information of plants used for the treatment of cough associated with respiratory diseases; local name, used plant part(s) and preparation method. Bio-data of the participants including their age, gender, residence, occupation, and educational background were also recorded. The participants were purposively selected comprising herb-sellers, traditional medical practitioners (herbalist), farmers, and hunters in the area. They were informed of the concept of the study in order to seek their consent and willingness to participate in the survey. The participants were individually questioned on their knowledge of using plant species to treat cough associated with respiratory diseases. Ten native field assistants were engaged to administer and interpret the questions to the participants in their local language (Yoruba) in order to facilitate efficient communication.

Plant Collection and Identification
The plant species were initially identified using their local 'Yoruba' names and later matched with their respective scientific classifications through consultation of relevant literature [32], while the current taxonomic classification was validated using "The Plant List" [43]. The voucher specimens were prepared, identified and authenticated by an expert prior to depositing at the Forest Herbarium, Ibadan (FHI), Oyo State, Nigeria.

Ethnobotanical Data Analysis
The information (for e.g., plant name and plant part used to treat cough associated with respiratory diseases) obtained through the ethnobotanical interviews were analyzed. In order to establish the importance of the documented plants used in treating cough associated with respiratory diseases, we analysed the data using the following ethnobotanical indices.
Based on the methods described by Tardío and Pardo-de-Santayana [44], we evaluated the Relative frequency of citation (RFC) for plant species mentioned in the study area.
where FC = frequency of citation/mention, N = Number of participants in the survey.
In an attempt to determine the preference of a particular plant species for the treatment of cough in the study area, the fidelity level (FL) was calculated as described by Friedman et al. [45]. High FL indicates high usage of a plant for cough while low FL denotes a low frequency for this condition.
where lp = number of participants that claimed a use of certain plant species to treat a cough, Iu = total number of participants in the survey.

Ethical Consideration
The study area is within the jurisdiction to the research study zones of Forestry Research Institute of Nigeria [46], a national research platform. The study was approved by the research coordinating unit of FRIN. All the participants provided verbal consent prior to data collection.

Inventory of Plant Species Used against Cough Associated with Respiratory Diseases
In the current study, 87 locally used medicinal plant species from 39 families were recorded for the treatment and management of cough associated with respiratory diseases in the study area (Table 2 and Appendix A). The relative high number of plant species is an indication of the rich flora available for managing cough associated with respiratory conditions among the community members. In view of the diverse etiology of cough, it remains one of the commonest symptoms associated with clinic/hospital visits in many developed countries [6]. Although the epidemiological studies on cough are currently scanty in sub-Saharan Africa [8], it remains one of the conditions that are treated with African medicinal plants [24,25,29,35,47,48]. For instance, cough ranked (5th) among the top 10 diseases commonly treated with medicinal plants among the 930 households sampled in Akwa Ibom State of Nigeria [49]. A study conducted among the rural people in northern Maputaland (South Africa) by York et al. [27], specifically identified cough as a common symptom that is often treated with medicinal plants used for respiratory diseases. Similarly in South Africa, an estimated 37% (2nd to tuberculosis which was the highest at 40%) of the 306 plants used for managing respiratory diseases by traditional healers were targeted at mitigating cough [50]. As revealed by Bekalo et al. [51], cough is a condition that is treated with different medicinal plants by the local people in the lowlands of Konta Special Woreda in Ethiopia. Furthermore, cough was the most common respiratory-tract infection managed using plant species in Mauritius [26]. Beyond Africa, similar utilisation of medicinal plants for counteracting cough have been documented in countries such as India [52], Spain [53], Greece [54], and Yemen [55]. As demonstrated in these aforementioned examples, there is continuous and widespread utilisation of medicinal plants for mitigating cough as a condition and as part of associated symptoms in many diseases especially those affecting the respiratory system.
The family Fabaceae was the most represented for the 87 plant species documented as remedy against cough associated with respiratory diseases (Figure 2). The number of plant species from the family Fabaceae was two-fold higher when compared to the next family with a high number of plants. Five (5) plant families including Asteraceae, Curcurbitaceae, Euphorbiaceae, Malvaceae, and Poaceace had four to five plant species while an estimated 49% of the 39 families had one representative member each. The dominance of the Fabaceae as the most common family to have been widely observed in several ethnobotanical surveys in Nigeria [34,47,56] and other countries in Africa countries [28,51,57,58]. Evidence to support the dominance of Fabaceae as a plant family with medicinal value was recently hypothesized by Van Wyk [59]. This assertion was based on the analysis of 4576 vascular plant species from 1518 genera that are used in Traditional African Medicine in sub-Saharan Africa. In addition, the Fabaceae with other families such as Apocynaceae, Burseraceae and Rubiaceae ranked as the most commonly-traded African medicinal plant species, an indication of commercial value. The popularity and high preference of the members of the family Fabaceae in African Traditional Medicine may be attributed to their availability and abundance as well as adaptability to different environments [56]. Plants 2020, 9,

Diversity and Ethnobotanical Indices of Plant Species Used Against Cough Associated with Respiratory Diseases
Despite the relative high number of plants utilised for cough purpose, their ethnobotanical indices including FC (1-12), RFC (0.01-0.12) and FL (1-40%) were generally low (Table 2). Furthermore, approximately 89% of the plant species had relatively lower indices (for e.g., FC ≤ 3; RFC ≤ 0.03, FL ≤ 3%) when compared to other plants used for cough. In the study area, Crinum jagus was the most popular plant used for cough among the participants. Member of the genus Crinum have been extensively utilised among diverse diseases in folk medicine globally and an increasing interest from pharmaceutical sector based on the therapeutic potential [60]. Locally known as 'Ogede odo', Crinum jagus has long been regarded as a potent remedy for relieving asthma and related cough among the Yoruba of south-western part of Nigeria [30,31]. Member of the genus Crinum are known to often be used for diverse ailments including respiratory diseases in Democratic Republic of the Congo [24,25], Ethiopia [61], Nigeria [47], and Cameroon [62]. The alkaloidal constituents, which are often characteristically of the family Amaryllidaceae including the genus Crinum, are known to significantly contribute to their diverse medicinal attributes [60].

Diversity and Ethnobotanical Indices of Plant Species Used against Cough Associated with Respiratory Diseases
Despite the relative high number of plants utilised for cough purpose, their ethnobotanical indices including FC (1-12), RFC (0.01-0.12) and FL (1-40%) were generally low (Table 2). Furthermore, approximately 89% of the plant species had relatively lower indices (for e.g., FC ≤ 3; RFC ≤ 0.03, FL ≤ 3%) when compared to other plants used for cough. In the study area, Crinum jagus was the most popular plant used for cough among the participants. Member of the genus Crinum have been extensively utilised among diverse diseases in folk medicine globally and an increasing interest from pharmaceutical sector based on the therapeutic potential [60]. Locally known as 'Ogede odo', Crinum jagus has long been regarded as a potent remedy for relieving asthma and related cough among the Yoruba of south-western part of Nigeria [30,31]. Member of the genus Crinum are known to often be used for diverse ailments including respiratory diseases in Democratic Republic of the Congo [24,25], Ethiopia [61], Nigeria [47], and Cameroon [62]. The alkaloidal constituents, which are often characteristically of the family Amaryllidaceae including the genus Crinum, are known to significantly contribute to their diverse medicinal attributes [60].      In addition to Crinum jagus, Anacardium occidentale and Khaya grandifoliola (FC = 11; RFC = 0.11; FL = 11%) as well as seven plants (Abrus precatorius, Aframomum melegueta, Bridelia ferruginea, Citrus aurantifolia, Garcinia kola, Jatropha curcas, Jatropha multifida, Cymbopogon citratus, Ageratum conyzoides and Alstonia boonei with FC = 10; RFC = 0.1; FL = 10%) were the 10 most common plants used as cough remedy in the study area (Table 2). According to Sonibare and Gbile [31], herbalists and traditional medical practitioners recognised the majority of these aforementioned plants as remedy against asthma and other respiratory conditions in Nigeria.
From the current findings, an estimated 46% and 43% of the plant species have been reported for respiratory-related conditions in Nigeria and other countries, respectively ( Table 2). Some of these plants are known to be used for treatments of cough and associated respiratory diseases/conditions (for e.g., asthma, expectorant, tuberculosis and bronchitis) in at least 15 countries globally. For instance, the use of Psidium guajava for the treatment of cough has been documented in Pakistan [63], Uganda [64,65], South Africa [27], and Zimbabwe [66]. On the other hand, Garcina kola has been extensively documented as a cough remedy in Nigeria [29,36,49] but no record has been found in other parts of the world. Furthermore, reports of the use of approximately 32% of the plants such as Corchorus olitorius, Hybanthus enneaspermus and Theobroma cacao as cough remedy in folk medicine were not found ( Table 2). These findings clearly establish the existence of some degree of similarities and uniqueness with regards to the use of plants for treating and managing common ailments among different ethnic groups globally.

Life-Forms and Plant Parts Used against Cough Associated with Respiratory Diseases
In the study area, trees had the highest proportion (37%) while climbers were the lowest life-form for the plant species used for treating cough associated with respiratory problems (Figure 3). The dominance of woody plants (trees and shrubs) was evidence as they accounted for approximately 61% of the plants documented. The popularity of woody perennials for cough remedy may be attributed to the rain forest nature of the location. The strong relationship between the prevailing local flora corresponds to the dominant life-form use for medicinal purpose among community members [28,51,57,58]. Ethnobotanical survey conducted in Ekiti State, which is within the same rain forest vegetation in south west of Nigeria, also indicated the dominance of woody plants for medicinal purposes among the local communities [34]. Herbaceous plant was relatively (3rd most dominant life-form) popular among the participants (Figure 3). The popularity of herb has been widely reported as a common remedy for asthma and related conditions in South Africa [28]. Furthermore, an analysis of 306 plants used for treating and managing respiratory infections and related symptoms in South Africa revealed the dominance of herbs (40.2%) which was followed by trees (35.6%) and shrubs (23.9%) as the common life-forms [50]. Likewise, Alamgeer et al. [20] indicated the dominance of herbs (57%) based on the analysis of 384 plant species used for or respiratory diseases in Pakistan. However, the seasonality that is associated with the occurrence of herbs remain a major challenge in terms of their utilisation for common ailments including cough.
As reported by the participants, diverse plant parts such as leaves, stem-bark, seeds, fruits, nuts, bulbs, and latex were utilised for managing cough in the study area ( Figure 4). However, leaves (36%) were the major plant part used as a cough remedy. Factors such as ease of accessibility, availability and relative abundance of leaves often justify their dominance in traditional medicine [50,55]. Consequently, several ethnobotanical studies have observed the wide-spread utilisation of leaves for preparing herbal medicine for diverse diseases affecting humans [26,27,48,50,[55][56][57]. The harvesting and utilisation of leaves or similar flora components such as fruits and seeds are often considered less destructive or detrimental to plant survival when compared to plants such as bulbs and bark [21]. From a conservation perspective, the plant species used for cough remedy in the study area are less likely to suffer from extensive population decline if continuously done in a sustainable manner.
Consequently, several ethnobotanical studies have observed the wide-spread utilisation of leaves for preparing herbal medicine for diverse diseases affecting humans [26,27,48,50,[55][56][57]. The harvesting and utilisation of leaves or similar flora components such as fruits and seeds are often considered less destructive or detrimental to plant survival when compared to plants such as bulbs and bark [21]. From a conservation perspective, the plant species used for cough remedy in the study area are less likely to suffer from extensive population decline if continuously done in a sustainable manner.

Method of Preparation and Administration of Plant Species Used Against Cough Associated with Respiratory Diseases
Even though the participants identified eight methods used for preparing the medicinal plants for managing cough in the study, the majority (approximately 40%) were prepared as decoction

Method of Preparation and Administration of Plant Species Used against Cough Associated with Respiratory Diseases
Even though the participants identified eight methods used for preparing the medicinal plants for managing cough in the study, the majority (approximately 40%) were prepared as decoction ( Figure 5). In terms of the administration, all the preparations were administered orally in the study area. The popularity of decoction as a means of preparing medicinal plants for respiratory diseases was also reporting in a survey conducted in Mauritius by Suroowan and Mahomoodally [26]. Generally, decoction and infusion are often the popular means of preparing medicinal plants in local communities [20,57,64]. This may be attributed to the simplicity involved in the process whereby decoction implies the heating or boiling of the plant material in water while infusion is made by suspending the plant material in cold or pre-warmed water [26]. This described process may vary in terms of factors such as the amount of water and duration of the boiling among the different traditional healers and communities [57]. Given that these different variables influence the efficacies of the medicinal plants, the issue of adequate standardization deserves more attention from all stakeholders in traditional medicine.

Sources of Plant Species Used Against Cough Associated with Respiratory Diseases
Most of the plant species used for the treatment of cough associated with respiratory diseases in the study area were collected from the wild populations ( Figure 6). The heavy reliance on the wild populations of plants for medicinal purposes is well-enriched in African culture as demonstrated in several ethnobotanical survey [35,56,57]. Given that the dependence on wild population of useful plants is not sustainable over-time, the need to devise a means of mitigating this challenge has been strongly recommended [21]. For instance, adequate protection of some species can be achieved through increased enactment and implementation of appropriate laws and regulation as well as the introduction of sustainable wild harvesting methods. Traditional healers and community members are strongly encouraged to be actively involved in domestic cultivation of essential and widely-used plant species. Thus, it is commendable that some of the plants used as cough remedy are currently being cultivated in the study area (Figure 4). Similar evidence of sourcing useful plants used against different diseases has been reported by other researchers in countries such as Nigeria [56], Mauritius Most of the plant species (for e.g., Ananas comosus, Garcinia kola and Citrus aurantifolia) identified were used singly, few species were in multi-herbal combinations, while in some rare cases preparations were in herbal syrup (Appendix A). In African Traditional Medicine, combining different part(s) of plants and/or plant species are common practice for treating diverse diseases [31,[80][81][82].

Sources of Plant Species Used against Cough Associated with Respiratory Diseases
Most of the plant species used for the treatment of cough associated with respiratory diseases in the study area were collected from the wild populations ( Figure 6). The heavy reliance on the wild populations of plants for medicinal purposes is well-enriched in African culture as demonstrated in several ethnobotanical survey [35,56,57]. Given that the dependence on wild population of useful plants is not sustainable over-time, the need to devise a means of mitigating this challenge has been strongly recommended [21]. For instance, adequate protection of some species can be achieved through increased enactment and implementation of appropriate laws and regulation as well as the introduction of sustainable wild harvesting methods. Traditional healers and community members are strongly encouraged to be actively involved in domestic cultivation of essential and widely-used plant species. Thus, it is commendable that some of the plants used as cough remedy are currently being cultivated in the study area ( Figure 4). Similar evidence of sourcing useful plants used against different diseases has been reported by other researchers in countries such as Nigeria [56], Mauritius [26], Ghana [57], and Greece [54]. The application of biotechnological techniques also has the potential to contribute to the sustainability and commercialization of the valuable floras that are currently utilised among different ethnic groups for diverse diseases in Africa [17,21].

Conclusions
In the current study, we documented the use of 87 plant species for the management of cough associated with respiratory diseases in Ede South Local Government Area, Osun state, Nigeria. This suggests that the use of plants remain popular for treating common ailments in the study area. Similarity in the use of some plants when compared to other studies in Nigeria and other parts of the world was also established. However, a substantial (about 32%) portion of the documented plant species for management of cough indicates the rich indigenous knowledge on plant resources in the study area. The study also revealed the high dependence (63%) on the wild populations for plant materials by the local community. Given the unsustainable nature of this practice, the incorporation of cultivation and other sustainable approaches (for e.g., plant part substitution, use of leaves instead of roots/bark, where possible) to mitigate decline and eventually loss of these plants is strongly recommended. Taken together, the current findings on the medicinal uses of plant species for cough provides baseline information for future biological efficacy testing and possible isolation of biological active compounds for managing/treating cough and associated respiratory conditions as well as expectorant.

Conclusions
In the current study, we documented the use of 87 plant species for the management of cough associated with respiratory diseases in Ede South Local Government Area, Osun state, Nigeria. This suggests that the use of plants remain popular for treating common ailments in the study area. Similarity in the use of some plants when compared to other studies in Nigeria and other parts of the world was also established. However, a substantial (about 32%) portion of the documented plant species for management of cough indicates the rich indigenous knowledge on plant resources in the study area. The study also revealed the high dependence (63%) on the wild populations for plant materials by the local community. Given the unsustainable nature of this practice, the incorporation of cultivation and other sustainable approaches (for e.g., plant part substitution, use of leaves instead of roots/bark, where possible) to mitigate decline and eventually loss of these plants is strongly recommended. Taken together, the current findings on the medicinal uses of plant species for cough provides baseline information for future biological efficacy testing and possible isolation of biological active compounds for managing/treating cough and associated respiratory conditions as well as expectorant.

Conflicts of Interest:
We do not have any competing interest regarding this research. The opinionsand conclusions/recommendations expressed in this work are that of the authors, and that the funder accepts no liability whatsoever in this regard.